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Prop balance - weight location
- Thread starter kritsher
- Start date
rv7charlie
Well Known Member
Not telling you what to do, but I just use longer screws on the backplate perimeter. An oversize nut is a convenient shim/weight to clear the nutplate, and then nut/washer(s) as needed.
A lot of guys put the weight on the holes in the ring gear (flywheel), but that's a bit of an offset from the imbalance.
edit: Never paid attention to a -12 spinner; don't know if the techniques will work there. Obviously the ring gear is out...
Charlie
A lot of guys put the weight on the holes in the ring gear (flywheel), but that's a bit of an offset from the imbalance.
edit: Never paid attention to a -12 spinner; don't know if the techniques will work there. Obviously the ring gear is out...
Charlie
My mechanic just put stick on wheel balance weights on the backing plate flange. Haven?t moved in 300 hrs.
Jack
Jack
That's a very risky, un-approved way to balance and I would never do it, drill the backplate and install weights using standard hardware is standard practice. On a Lyc you can mount them on the flywheel but the 12 obviously has no such thing.
My A&P drilled a hole and installed a small machine screw for the weight.
Skunkworks
Active Member
My A&P drills holes into spinner bulkhead too
Just had this done for a second time due to having hub half being replaced and experiencing vibrations. Recommend everyone get this done. This time around Dave got it to .1 and boy is it smooth running. Jane now has 948hrs and gearbox inspection is coming up at 1000 hrs will see the results on the gears.
Just had this done for a second time due to having hub half being replaced and experiencing vibrations. Recommend everyone get this done. This time around Dave got it to .1 and boy is it smooth running. Jane now has 948hrs and gearbox inspection is coming up at 1000 hrs will see the results on the gears.
Do it often
I agree, most folks would be surprised at how much smoother the whole unit is after a balance. You should dynamically balance whenever there has been a change in the rotating assembly, which would include anything from a simple prop pitch change or replacing the spinner to overhauling the engine or gearbox.
Most manufacturers limit vibration to 0.25 IPS, but it only takes about 0.07 inches per second to be noticeable by the average person. When I did my first balance check on my RV12 last year, it was at 0.68 IPS. Reindexing the prop and spinner brought it down to 0.47, but that's still a destructive amount of vibration over time. I now have it at 0.01 IPS.
My hangar neighbor has a C150 with an O-200 and he said it has run smooth that way for years. I offered to do a check for him and found 0.32 IPS, which shocked him. We've now got his down to 0.02 IPS and he says it's like a new airplane. So, even if you think it's smooth, I highly recommend getting at least a balance check - you might be surprised what the meter shows.
I agree, most folks would be surprised at how much smoother the whole unit is after a balance. You should dynamically balance whenever there has been a change in the rotating assembly, which would include anything from a simple prop pitch change or replacing the spinner to overhauling the engine or gearbox.
Most manufacturers limit vibration to 0.25 IPS, but it only takes about 0.07 inches per second to be noticeable by the average person. When I did my first balance check on my RV12 last year, it was at 0.68 IPS. Reindexing the prop and spinner brought it down to 0.47, but that's still a destructive amount of vibration over time. I now have it at 0.01 IPS.
My hangar neighbor has a C150 with an O-200 and he said it has run smooth that way for years. I offered to do a check for him and found 0.32 IPS, which shocked him. We've now got his down to 0.02 IPS and he says it's like a new airplane. So, even if you think it's smooth, I highly recommend getting at least a balance check - you might be surprised what the meter shows.
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Hopefully you mean .01
.1 is not horribly bad but when paying a professional do it, they should be able to get it very close to .01.
BTW, the acceleration value that is considered noticeable is .07 or higher (not .7)
The below chart is generally considered the "standard" values for balancing.
My goal is 0.050 IPS or better when balancing, .010 is very seldom obtainable on professional balancing equipment.
I've done balance checks after Dynavib balances and other "hobby" balancers and my numbers are always higher (I can't even get .01x on my own aircraft after multiple attempts). I have had a few over the years that got into the .01x range but after hundreds of balance jobs I can assure you that .01x is generally impossible to achieve (notice my equip goes out 3 places while most only go 2 places)
What some of the manufactures say:
Unless otherwise specified by the engine or airframe manufacturer, Hartzell
recommends that the propeller be dynamically balanced to a reading of 0.2 IPS,
or less.
Most dynamic balance equipment manufacturers specify 0.15 - 0.2 ips as being an
acceptable level. McCauley Propeller Systems agrees that 0.15 - 0.2 is an acceptable
level, but our experience has shown that 0.07 ips or lower is noticeably smoother.
DANGER — 1.25 Inches Per Second (IPS) Peak Amplitude. The propeller should be removed and a static balance performed.
VERY ROUGH — 1.00 Inches Per Second (IPS) Peak Amplitude. Propeller can be dynamically balanced; however a large amount of weight will be required. A propeller static balance is recommended. Operation at this vibration level could cause damage.
ROUGH --- 0.50 Inches Per Second (IPS) Peak Amplitude. Propeller definitely requires dynamic balance. Long term operation at this vibration level could cause excessive wear.
SLIGHTLY ROUGH -- 0.25 Inches Per Second (IPS) Peak Amplitude. Dynamic balance will improve passenger comfort.
FAIR---- 0.15 Inches Per Second (IPS) Peak Amplitude. This is the maximum acceptable vibration level after dynamic balancing.
GOOD ---- 0.07 Inches Per Second (IPS) Peak Amplitude. Vibration levels below 0.07 will not be detectable by pilots or passengers.
My goal is 0.050 IPS or better when balancing, .010 is very seldom obtainable on professional balancing equipment.
I've done balance checks after Dynavib balances and other "hobby" balancers and my numbers are always higher (I can't even get .01x on my own aircraft after multiple attempts). I have had a few over the years that got into the .01x range but after hundreds of balance jobs I can assure you that .01x is generally impossible to achieve (notice my equip goes out 3 places while most only go 2 places)
What some of the manufactures say:
Unless otherwise specified by the engine or airframe manufacturer, Hartzell
recommends that the propeller be dynamically balanced to a reading of 0.2 IPS,
or less.
Most dynamic balance equipment manufacturers specify 0.15 - 0.2 ips as being an
acceptable level. McCauley Propeller Systems agrees that 0.15 - 0.2 is an acceptable
level, but our experience has shown that 0.07 ips or lower is noticeably smoother.
DANGER — 1.25 Inches Per Second (IPS) Peak Amplitude. The propeller should be removed and a static balance performed.
VERY ROUGH — 1.00 Inches Per Second (IPS) Peak Amplitude. Propeller can be dynamically balanced; however a large amount of weight will be required. A propeller static balance is recommended. Operation at this vibration level could cause damage.
ROUGH --- 0.50 Inches Per Second (IPS) Peak Amplitude. Propeller definitely requires dynamic balance. Long term operation at this vibration level could cause excessive wear.
SLIGHTLY ROUGH -- 0.25 Inches Per Second (IPS) Peak Amplitude. Dynamic balance will improve passenger comfort.
FAIR---- 0.15 Inches Per Second (IPS) Peak Amplitude. This is the maximum acceptable vibration level after dynamic balancing.
GOOD ---- 0.07 Inches Per Second (IPS) Peak Amplitude. Vibration levels below 0.07 will not be detectable by pilots or passengers.
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I agree. That is why I said a pro should be able to get close to .01.
I regularly get final values of .02 or .03 (though not meaning to imply I am a pro.... I only do 3 or 4 per year)
Actually, by the time the weight was mounted on the spinner backing plate it was .02.
MicroVib II, I only use the front accel to balance the prop, if you want to mount a rear you can but nothing you can do to really change that so it pretty much a waste of time unless you have a internal engine vibration you are trying to diagnose.
This just seems like such a good idea, I wonder why more people don't do this? Not to mention it's at the outside of the spinner bulkhead, has 14 positions on my spinner, and will eliminate the need to remove and re-install the spinner each time you do a run.
Only downside is when removing the spinner I'd need to remove the top cowl to get access to the added HW. It's pretty rare that I need to remove my spinner without removing the cowl - I only did this when adjusting the prop's fine pitch stop during early flight testing.
These are the sources of information I reference when balancing propellers. I use a Dyna Vibe GX3 so the equipment in these publications is different but the principles are the same and the mounting of balance weight are best practices.
For your reading pleasure google the following 3 publications:
FAA Advisory Circular 20-37E - Aircraft Propeller Maintenance
The following is a quote from the above AC and both use best practices according to the FAA.
"When approved aircraft or propeller manufacturer’s procedures are not available, there are other acceptable dynamic propeller balancing procedures. These include, but are not limited to the Chadwick-Helmuth Publication No. AW-9511-2, entitled “The Smooth Propeller”, and ACES Publication No. 100-OM-01, entitled “ACES Systems Guide to Propeller Balancing”. "
Of course, if you fly an experimental you are free to "experiment"
.07 ips is considered balanced. Really the only way to tell the difference between .01 and .07 ips is by using pro-grade balancing equipment.
For your reading pleasure google the following 3 publications:
FAA Advisory Circular 20-37E - Aircraft Propeller Maintenance
The following is a quote from the above AC and both use best practices according to the FAA.
"When approved aircraft or propeller manufacturer’s procedures are not available, there are other acceptable dynamic propeller balancing procedures. These include, but are not limited to the Chadwick-Helmuth Publication No. AW-9511-2, entitled “The Smooth Propeller”, and ACES Publication No. 100-OM-01, entitled “ACES Systems Guide to Propeller Balancing”. "
Of course, if you fly an experimental you are free to "experiment"
.07 ips is considered balanced. Really the only way to tell the difference between .01 and .07 ips is by using pro-grade balancing equipment.
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Thanks Ray - looking at my Hartzell manual it says to put the weights on the spinner bulkhead, outside of the doubler and inboard the flange. Looks like that's what I'll do!
Perfect timing tho. I did mine today!
I have the Dyna Vibe Classic and mount what usually is a 1/4 bolt and washers to center of rear spinner plate. I do three runs and average them. I made a protractor that I slide onto pitot tube to find the spot to add wt... I had done a vibe run yester that averaged .70...after adding just 8 grams which was a short 1/4 bolt and two washers I got it down to .05...also don't forget to make sure your transduce is tight and you have balanced your carbs first...I was surprised at only needing 8 grams, I've added 25g before to get from .5 to .05...the difference is notable.
The plates are static balance weights which are left alone.
I don't think they actually showed where they placed the final wts.
Nice to see they use the same equipment I use.
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TParker
Well Known Member
Those particular weights are specific to our designs as they fit to the hub(s). We've got other, similar, ones for other propeller systems. We may also use washers under those fillister screws, or the screws themselves. They are initial configured as part of the static balance before leaving the factory.
McCauley has similar type of model specific weights that attach to their forward cap ring (rough description, not sure of the official McCauley term); so same idea but different implementation.
Those are the static balance weights, but we do sometimes alter them as part of a dynamic balance. There are several notes about this in the dynamic balance Maintenance Practices section of the relevant propeller Owner's Manual. If I recall correctly, in the linked video example, additional weights were not required.
Otherwise, we tend to add weights (screws, washers, etc.) to locations on the spinner bulkhead, many of our factory spinner bulkheads have nut plates preinstalled for this express purpose.
Thanks Trevor. I just balanced mine down to about 0.02 at 2004 RPM and 0.05 at 2407 RPM using nuts, bolts, and washers on the flywheel. It seems like nutplates on the spinner make a lot more sense when you get down to those last half-gram suggestions.
